Differential pressure transducer

ABSTRACT

A housing structure defines opposing sealed fluid pressure chambers separated by a thin flexible metal diaphragm formed integrally with a surrounding retaining ring and a narrow thickened beam portion extending radially across the diaphragm. A small cavity is formed extending into one end of the beam portion. Strain gages, electrically coupled as a differential bridge circuit, are applied to opposite walls of the cavity in the area of maximum bending stress to measure the compresson strain on one wall and the tension on the other resulting from deflection of the diaphragm and its beam portion by pressure differences in the opposing chambers.

United States Patent 1 Bice et al.

[ DIFFERENTIAL PRESSURE TRANSDUCER [75] Inventors: James W. Bice, Wayne,N.J.; Will Timm, deceased, late of Flintridge, Calif. by Asta Timm,executrix [73] Assignee: Celesco Industries, Inc., Costa Mesa,

' Calif.

[22] Filed: Nov. 11, 1971 [21] Appl. No.2 197,878

[52] US. Cl. 73/398 AR, 338/4, 338/42 [51] Int. Cl. G011 9/04 [58] Fieldof Search 73/398 AR, 406, 407 R;

[56] References Cited UNITED STATES PATENTS 3,035,240- 5/1962 Starr338/4 3,315,201 4/1962 Werme 338/42 Primary Examiner-Donald O. WoodielAttorney-Tipton D. Jennings [57] ABSTRACT A housing structure definesopposing sealed fluid pressure chambers separated by a thin flexiblemetal diaphragm formed integrally with a surroundingretaining ring and anarrow thickened beam portion extending radially across the diaphragm. Asmall cavity is formed extending into one end of the beam portion.Strain gages, electrically coupled as a differential bridge circuit, areapplied to opposite walls of the cavity in the area of maximum bendingstress to measure the compresson strain on one wall and the tension onthe other resulting from deflection of the diaphragm and its beamportion by pressure differences in the opposing chambers.

10 Claims, 5 Drawing lFigures PATENTEDHBT 'zma SHEET 2 OF 2 DIFFERENTIALPRESSURE TRANSDUCER BACKGROUND OF THE INVENTION This invention relatesto transducers and, more particularly, to strain gage differentialpressure transducers adapted to detect differences in pressure forcesapplied to opposite sides of a diaphragm structure.

Transducers of this type are often required to monitor pressuredifferentials in a fluid medium that might damage or destroy the sensingelements employed. For example, pressure differences between two pointsin a process stream carrying corrosive chemicals may be monitored. Inthe past, transducers employing two diaphrams have been required toisolate the sensing elements from such damaging mediums. In suchtransducers, a layer or fill of oil may be provided between the twodiaphragms with the sensing elements mounted on the inner surface of onediaphragm within the oil fill so that the corrosive chemicals may thenimpinge against the outer sides of the two diaphragms without damagingthe sensing elements.

However, errors are introduced in such systems be cause static linepressures tending to compress the diaphragms and the enclosed oil filldecrease transducer sensitivity and accuracy. Furthermore, astemperature decreases, the oil may become more viscous, thus slowing thetransducer response time at low temperatures.

The present invention overcomes the difficulties of these priortransducers while at the same time being less expensive to manufacture.

SUMMARY OF THE INVENTION A transducer housing structure provides twomutually isolated fluid pressure chambers separated by a unitaryflexible diaphragm structure containing a small cavity into the flexiblestructure. Sensing means are mounted on interior surfaces of thecavitywhere substantial bending occurs to detect and measure deflectionsof the structure. The sensing means are sealed from the two chambers sothat opposite sides of the flexible diaphragm are exposed to the fluidpressure medium without contacting or damaging the sensing means.

In the preferred embodiment, the housing structure has two end platemembers held in place on opposite sides of an outer retaining ring. Theflexible diaphragm structure has a .thin circular metal diaphragm formedwith a cylindrical diaphragm support ring around its periphery and witha narrow thickened beam portion extending radially across the diaphragm.The diaphragm,

' beam portion and support ring are formed as one integral unit. Bothend plates have inner surfaces formed to match thecontour of theadjacent surfaces of the flexible diaphragm and beam. These inner endplate surfaces are positioned in close proximity to the flexible memberto serve as mechanical stops on both sides of the flexible memberlimiting the maximum deflection which could otherwise result inpermanent defor mation or destruction of the flexible diaphragm. Theouter retaining ring is held rigidly in place between the two end plateswith a pressure seal at each end. Each end plate has a central inletopening for conducting the fluid medium into the fluid pressure chamberformed between its inner surface and the adjacent surface of thediaphragm. The cavity is drilled in the retaining ring to extend intoone end of the beam,-and strain gage sensing elements are secured toopposite interior walls of the cavity. When the diaphragm and beam aredeflected by a differential pressure, these interior cavity walls, alongwith the attached strain gages are placed in tension or compression,according to the direction and amplitude of the diaphragm deflection.

In certain applications, holes are provided in the cylindrical walls ofthe diaphragm support ring so that its outer wall surfaces are subjectedto the same pressure as one of the chambers. One end of the diaphragmring is sealed against its end plate to isolate the other chamber. Thepressure on the outside of the retaining ring counters that on theinside of the diaphragm ring which with high static line pressures tendsto be forced outwardly, thus stretching the diaphragm and rendering itless sensitive to small pressure differences.

BRIEF DESCRIPTION OF THE DRAWING Other advantages and features of theinvention will be understood from the detailed description taken inconjunction with the figures of the drawing wherein:

FIG. 1 is a plan view of one embodiment of the invention;

FIG. 2 is a cross-sectional elevational view taken along the line 2--2of FIG. 1;

FIG. 3 is a cross-sectional elevational view taken along line 3-3 ofFIG. 2;

FIG. 4 is an enlarged cross-sectional perspective view of a portion ofthe embodiment shown in FIG. 2; and

FIG. 5 is a perspective view of a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION In a preferred embodiment of theinvention, as shown in FIGS. 1 and 2, the transducer housing has twocylindrical end plates 12 and 14 both having inner cylindrical endportions providing substantially flat circular interior surfaces 13 and15 respectively. Each end plate also has an integral larger diameterouter flange portion defining opposed flat annular inner surfaces 16 and17 around the periphery of the two end plates. An outer retaining ring18, formed as a thick walled hollow cylinder, has its flat annular endsurfaces clamped tightly between the surfaces 16 and 17 when the two endplates 12 and 14 are secured together. Outer retaining ring 18 acts tospace apart the inner adjacent surfaces 13 and 15 of the end plates 12and 14 by a precise amount to provide clearance for the diaphragm 30.

Threaded counter sunk holes 20 in the retaining ring 18 and the outerflange portions of end plates 12 and 14 are aligned to receive screws 22which are tightened to securely hold the end plates 12 and 14 tightlyagainst the retaining ring 18 and at the same time to provide a precisegap 24 between the inner surfaces 13 and I5 sufficient to receive thediaphragm 30. Of course, other methods such as welding may be employedto secure the end plates, the retaining ring, and the diaphragm ring 36together. The outer retaining ring 18 has hard rubber 0-rings 19positioned in its notched interior edges to seal against the adjacentsurfaces 16 and 17 of the end plates 12 and 14 respectively to preventloss of pressure and fluid from the housing.

Cylindrical bores or chambers 26 and 28 extend through the centralportion of the end plates 12 and 14 respectively and are threaded attheir outer ends for connection to two pressure lines from the pointsbetween which pressure differences are being monitored.

As has been described above, the end plate inner surfaces 13 and areseparated by a cylindrical gap 24 provided by the outer retaining ring18 spacing apart the two end plates 12 and 14. The gap 24 has anenlarged portion extending from one side of the gap 24 to the other inorder to provide clearance for the beam 32, to be described hereinafter.The two end plates and the retaining ring 18 together enclose adiaphragm subassembly that is mounted within the retaining ring 18between the end plates.

As may be seen in FIGS. 2 through 5, the diaphragm subassembly comprisesa thin flexible circular diaphragm 30, an integral narrow thickened beamportion 32 extending diametrically across both sides of the diaphragm30, and an integral annular diaphragm support ring 34 extending aroundthe outside periphery of the diaphragm 30.

The diaphragm 30 and beam 32 are formed equidistant between the ends ofthe diaphragm ring 34 and after assembly are positioned about midwaybetween the inner surfaces 13 and 15 of the end plates 12 and 14 ingap24 and in close enough proximity to the walls 13 and 15 so that thewalls serve as overload stops to prevent permanent deformation ordestruction of the diaphragm due to excessive pressure differentialsapplied to the diaphragm 30 through the chambers 26 and 28.

The diaphragm subassembly is preferably formed from a single piece ofmetal, and preferably from high grade stainless steel such as 17-4 Pl-Istainless steel. The diaphragm subassembly is precisely machined byelectronic discharge machining.

The diaphragm ring 34 fits snuggly between the flat inner surfaces 16and 17 inside the retaining ring 18. A hard rubber 0-ring 36 retained ina circular groove around one end of the diaphragm ring 34 provides aseal between the pressure chambers. The lower outer edge of thediaphragm ring 34 is cambered, as at 37, in order to prevent the lower0-ring 19 from forming a seal at that point. Preferably, the 0-ring 36seal is placed at the end of the diaphragm ring 34 that receives thelower static line pressure, with no seal at the high pressure end. Asshown in FIGS. 2 and 3, the 0-ring 36 is positioned between thediaphragm ring 34 and the end plate surface 16, thus making the upperend the low pressure side. Alternatively, the seal could be made on thehigh pressure side, and the camber 37 in that case could be provided atthe upper outer edge of the diaphragm ring 34.

The axial length of the diaphragm ring 34 is preferably slightly lessthan the axial length of the retaining ring 18 so that the 0-ring 36seals the low pressure end of the diaphragm ring 34 without exertingenough pressure to seal the high pressure end. This permits some leakagebetween the surface 17 and the diaphragm ring 34. Alternatively, groovesor holes 70 may be drilled through the lower end of the periphery of thediaphragm ring 34, as shown in FIG. 5, in order to facilitate fluidpressure communication between the interior and exterior of thediaphragm support ring 34.

A sea] is thus provided between the chambers 26 and 28 while at the sametime the fluid pressure in the chamber 28 is allowed to pass beneath thediaphragm ring 34 and to communicate with the outside of the diaphragmring between the outer retaining ring 18 and the diaphragm ring 34. Inthis manner, pressure is applied to both the inside and the outside ofthe diaphragm ring 34 to equalize the pressures applied to the inside ofthe diaphragm ring 34 which would otherwise stretch the diaphragm 30. Ifhigh pressure were applied to only the inside of the diaphragm ring 34,the diaphragm 30 would be placed under considerable tension and theamount of pressure required to deflect the diaphragm 30 would beincreased. This would result in slight changes in pressure goingunnoticed or being erroneously detected. Therefore, the fluid pressureis allowed to pass beneath the diaphragm ring 34 between the diaphragmring 34 and the lower end plate 14 so that the outside of the diaphragmring 34 will eventually be at the same high pressure as the chamber 28.Of course, a certain amount of pressure is required in chamber 28 inorder to force fluid between the lower end of the diaphragm ring 34 andthe end plate 14. However, the height of the diaphragm ring 34 is suchthat pressures which are incapable of forcing fluid to the outside ofthe ring 34 will not be high enough to stretch the diaphragm 30 by anamount sufficient to cause erroneous readings.

In another embodiment of the invention (not shown), a second 0-ring isprovided at the bottom of diaphragm ring 36 and the retaining ring 18and the diaphragm ring 34 are secured tightly together to prevent thepassage of fluid to the outside of the diaphragm ring 34. Thisembodiment of the invention is particularly useful where large changesin pressure are anticipated compared with the normal line pressure andtherefore any stretching of the diaphragm 30 due to the normal linepressure will be negligible compared with the high pressure changes tobe detected.

In one example of employing the diaphragm subassembly, a high normal orstatic line pressure of about 5,000 psi is to be applied to bothchambers 26 and 28. If the expected maximum differential in the linepressure to be measured is only of the order of about 25 psi, thediaphragm 30 and beam 32 might have a diameter of 1% inches and would bedeflected only about 0.0015 inches at the center when subjected to suchpressure differentials.

Where higher pressure differentials are expected so that sensitivity tosmall pressure differentials is not important, the entire diaphragm 30is thickened (not shown) to equal the thickness of the beam 32 so thatthe beam 32 is, in effect, eliminated. In that case, of course, the gap24 between the end plate surfaces 13 and 15 is widened to compensate forthe increased thickness of the diaphragm 30.

The diaphragm beam 32 is needed only to provide an enlarged portion atthe periphery of the diaphragm 30 for the small cavity 38'which isdrilled in one end of the beam 32 for the reception of strain sensitiveelements. The cavity 38, which communicates with the larger space 56formed partly in the diaphragm ring 34 and partly in the retaining ring18, extends into the interior of the diaphragm 30 and has top and bottomwalls parallel to the plane of the diaphragm.

As may best be seen in FIG. 4, two semiconductor strain gages 40 aremounted on the top wall of the cavity 38 and two semiconductor straingages 42 are mounted on the bottom wall of the cavity 38 with a suitableadhesive. The strain gages are mounted within the outer limits of thediaphragm 30 near to the intersection of the diaphragm 30 and diaphragmring 34 in order to take advantage of the high stress concentrationswhich occur in that region when the diaphragm 30 is deflected. A .flatannular terminal ring 44 is mounted on the outside of the cavity 38 witha suitable adhesive. The terminal ring 44 is composed of an electricalinsulating material, such as epoxy board or plastic.

The leads of the strain gage elements 40 and 42 pass through the centralopening in the terminal ring 44 and are electrically connected, bysoldering or the like, to metal terminal pads 46. Terminal pads 46,composed of copper or the like, are mounted on terminal ring 44 with asuitable-adhesive.

An annular metal sleeve 50 is fitted into an opening 46 in one side ofthe retaining ring 18. A tongue 52 of the sleeve 50 fits into acorresponding annular groove 54 in the diaphragm ring 34. A hard rubber0-ring 58 is positioned between the end of the tongue 52 and thediaphragm ring 34. A second hard rubber tl-ring 60 is positioned betweensleeve 50 and retaining ring 18. The sleeve 50 is slightly wider thanthe distance between the end of the groove 54 and the outside walls ofthe end plates so that when connector 62 is bolted into place to closethe opening 56, the sleeve 50 is forced inwardly against the 0-rings 58and 60. The 0- rings 58 and 60 are thus squeezed between the sleeve 50and a diaphragm ring 34 and between the sleeve 50 and the retaining ring18, thus isolating the semiconductor strain gages and their leads fromharmful chemicals and the like. 0-ring 60 also prevents the escape offluids from the housing between the retaining ring 18 and the sleeve 50.

Electrical connector socket 62 is mounted on one side of end plates 12and 14 by means of screws 64 securing the square flange 66 of theconnector 62 to the side wall of the outer retaining ring 18 around theoutside of the space 56. Electrical connector 62 provides a cover forthe space 56 thus sealing the space 56 and the cavity 38 from thesurrounding atmosphere. The terminals 46 are electrically connected toconnector pins 68 to receive signals from the strain gages 40 and 42.

All of the parts shown in the drawings are composed of metal, such asstainless steel, except the semiconductor strain gages 40 and 42, theterminal ring 44, and the 0-rings 19, 36, 58 and 60.

In operation, when fluid pressures are applied to the chambers 26 or 28,the pressure in the chamber 26 will be applied across the entire topsurface of the diaphragm 30 and the pressure in the chamber 28 will beapplied across the entire lower surface of the diaphragm 30. If thepressure applied to chamber 26 is different from the pressure applied tochamber 28, the total force on one surface of the diaphragm 30 willexceed the force on the opposite surface, thus producing a net force onone surface of the diaphragm which will deflect the diaphragm in a givendirection by an amount corresponding to the pressure differentialbetween the two chambers. As the diaphragm 30 and beam 32 are deflected,bending of the diaphragm at its periphery places one of the upper orlower walls of the cavity 38 in tension and the other wall incompression. These stresses in opposite walls of the cavity 50 aredetected by the strain gage elements 40 and 42.

For example, when greater pressure is applied to chamber 28 than tochamber 26, the diaphragm 30 deflects upwardly so that the strain gageelements on the lower wall of the cavity 40 are subjected to tensionwhile the strain gage elements on the upper wall of the cavity aresubjected to compression.

The leads of the strain gages are electrically interconnected to form. aconventional bridge circuit (not shown) in which the strain gageelements 40 on the upper wall of the cavity constitute two opposite armsof the bridge, while the strain gage elements 42 on the bottom wall ofthe cavity constitute the two other opposite arms of the bridge.Typically, a constant voltage or current power supply (not shown) isconnected across two first diagonally opposite input connection pointsof the bridge, with the output being obtained from the two otheropposite connection points. Temperature compensating circuitry may beemployed as needed, typically be connecting a temperature responsiveresistance across the power supply connection points in the bridge. Anoutput indicator, such as an oscilloscope, oscillograph, magnetic datarecorder, chart recorder, or galvinometer receives the output to recordor indicate the amplitude and variation of the pressure differentialbeing monitored.

The invention has been described in preferred forms with particularity,but this is only by way of example. Various changes in construction andapplication may be made without departing from the spirit or scope ofthe invention.

The invention claimed is:

1. A differential pressure transducer, comprising:

a housing having two fluid pressure chambers;

a flexible diaphragm separating said chambers, said flexible diaphragmhaving opposed surfaces and an internal cavity extending radiallyinwardly from an edge thereof between opposite diaphragm surfaces;

a diaphragm support ring formed integrally with the flexible diaphragmat its outer periphery, said diaphragm support ring having an insidesurface and an outer surface, said chambers communicating with oppositesurfaces of said flexible diaphragm and with the inside surface of saiddiaphragm support ring;

means for supplying fluid pressure from one of said chambers to theouter surface of said diaphragm support ring; and

strain sensing means mounted within said cavity in the plane of saidflexible diaphragm for detecting bending stresses resulting fromdeflections of said flexible diaphragm by differences in the fluidpressures applied to said chambers.

2. A transducer as defined in claim 1 wherein said sensing means arestrain gages mounted within said cavity near the outer periphery of saidflexible diaphragm on at least one wall of said cavity parallel to theplane of said flexible member, and further comprising means for sealingsaid cavity from said fluid pressure chambers.

3. A transducer, comprising:

a housing having two fluid pressure chambers;

a flexible diaphragm separating said chambers, said diaphragm havingopposed surfaces, one surface of said diaphragm communicating with oneof said chambers and the opposite surface of said diaphragmcommunicating with the other chamber, and having a cavity formed betweensaid surfaces to extend inwardly from one edge parallel to saidsurfaces;

a pressure seal between said two chambers;

a support formed around the outer edges of said flexible diaphragm, saidsupport having an inside and an outside, both of said chamberscommunicating with the inside of said support to minimize stretching ofsaid flexible diaphragm; and

a sensing element mounted within said cavity, said sensing element beingmounted parallel to the plane of said flexible diaphragm and beingadapted to detect deflections of said flexible diaphragm.

4. A transducer as defined in claim 3 wherein said flexible diaphragm isa thin metal diaphragm and said support means is an elongatedcylindrical diaphragm support ring formed integrally with said diaphragmto surround its edges, said diaphragm support ring having two ends, andwherein said seal comprises an O-ring between one end of said supportring and an interior surface of said housing.

and wherein said fluid pressure supplying means includes having theother end of said diaphragm ring not being sealed to permit fluidpressure in one of said chambers to be supplied to the outside of saiddiaphragm support ring.

5. A transducer as defined in claim 4 further comprising:

a narrow thickened beam portion formed integrally with said diaphragmand extending diametrically across said diaphragm, said cavity extendinginto one end of said beam.

6. A differential strain gage transducer, comprising:

a housing having first and second cylindrical end plates formed withopposing inner end surfaces, each having a central inlet bore extendingaxially therethrough;

an annular retaining ring secured between said end plates to space apartopposing inner end surfaces;

an integral diaphragm subassembly comprising a thin flexible diaphragm,an elongated diaphragm support ring fromed around the outer periphery ofthe diaphragm to support the edges and a narrow thickened beam portionextending diametrically across said diaphragm, said diaphragm beingmounted between said two end plates and spaced from said opposing innerend surfaces, opposite surfaces of said diaphragm and the adjacentinside surfaces of said diaphragm ring being in fluid pressurecommunication with the respective inlet bores and the outside of saiddiaphragm ring being in communication with one of said bores;

said subassembly being formed with an opening in said diaphragm ringextending radially from its outer periphery and terminating in a smallcavity extending radially into one end of said beam portion to defineopposing walls in a plane parallel to the plane of the diaphragm andextending into said beam; and

sensing elements secured to the top and bottom walls of said cavityadapted to detect deflections of said diaphragm due to differences inthe pressures applied through said bores to said diaphragm.

7. A transducer as defined in claim 6 wherein the opposing inner endsurfaces are formed on said end plates to match the contours of theadjacent surfaces of said diaphragm and beam portion and are closelyspaced therefrom to act as mechanical stops for said diaphragm.

8. A differential strain gage pressure transducer, comprising:

a housing having first and second cylindrical end plates, said endplates each having a flat inner end surface positioned closely adjacentthat of the other;

an outer retaining ring in the form of a thick walled cylindrical sleeveheld between an outwardly flanged outer end portion of said two endplates maintaining a predetermined spacing between said adjacent flatinner end surfaces;

means for securing said two end plates and said retaining ring togetherto form a rigid unit;

said end plates each having a central fluid inlet bore extending axiallyfrom the inner to the outer ends of each end plate;

an integral metal diaphragm subassembly comprising a thin flat flexiblecircular diaphragm, a narrow thickened beam portion formed on both sidesof said diaphragm and extending diametrically in the same directionacross opposite surfaces of said diaphragm, and an elongated annulardiaphragm sup port ring formed around the outer periphery of saiddiaphragm;

said diaphragm ring being clamped between said end plates so that thediaphragm is spaced substantially midway between said adjacent flatinner end surfaces of said end plates to define separate first andsecond fluid pressure chambers;

sealing means between at least one of said end plates and said diaphragmsupport ring for preventing fluid pressure communication between saidfirst and second fluid pressure chambers;

said diaphragm support ring being formed to define radial openingscommunicating between only one of said chambers and the exteriorsurfaces of said diaphragm support ring;

a small hollow cavity extending radially into one end of said beamportion and communicating externally through enlarged radial aperturesformed through the cylindrical walls of said diaphragm support ring andsaid outer retaining ring, said cavity providing opposite interior wallsparallel to the plane of said diaphragm;

a first pair of semiconductor strain gage elements attached to oneinterior wall of said cavity;

a second pair of semiconductor strain gage elements attached to theopposite interior wall of said cavity;

said first and second pairs of semiconductor strain gage elementsattached to said opposite interior walls being placed respectively intension and in compression by bending resulting from deflections of saiddiaphragm and said beam portion by fluid pressure differences in saidchambers; and

circuit means coupling said first and second pair of strain gageelements, with said enlarged apertures being adapated to receiveexternal input and output electrical connections thereto.

9. A transducer as defined in claim 2 wherein said fluid pressuresupplying means comprises a plurality of holes extending through saiddiaphragm support ring.

10. A transducer as defined in claim 3 wherein said fluid pressuresupplying means comprises a plurality of holes extending through saidsupport.

1. A differential pressure transducer, comprising: a housing having twofluid pressure chambers; a flexible diaphragm separating said chambers,said flexible diaphragm having opposed surfaces and an internal cavityextending radially inwardly from an edge thereof between oppositediaphragm surfaces; a diaphragm support ring formed integrally with theflexible diaphragm at its outer periphery, said diaphragm support ringhaving an inside surface and an outer surface, said chamberscommunicating with opposite surfaces of said flexible diaphragm and withthe inside surface of said diaphragm support ring; meAns for supplyingfluid pressure from one of said chambers to the outer surface of saiddiaphragm support ring; and strain sensing means mounted within saidcavity in the plane of said flexible diaphragm for detecting bendingstresses resulting from deflections of said flexible diaphragm bydifferences in the fluid pressures applied to said chambers.
 2. Atransducer as defined in claim 1 wherein said sensing means are straingages mounted within said cavity near the outer periphery of saidflexible diaphragm on at least one wall of said cavity parallel to theplane of said flexible member, and further comprising means for sealingsaid cavity from said fluid pressure chambers.
 3. A transducer,comprising: a housing having two fluid pressure chambers; a flexiblediaphragm separating said chambers, said diaphragm having opposedsurfaces, one surface of said diaphragm communicating with one of saidchambers and the opposite surface of said diaphragm communicating withthe other chamber, and having a cavity formed between said surfaces toextend inwardly from one edge parallel to said surfaces; a pressure sealbetween said two chambers; a support formed around the outer edges ofsaid flexible diaphragm, said support having an inside and an outside,both of said chambers communicating with the inside of said support tominimize stretching of said flexible diaphragm; and a sensing elementmounted within said cavity, said sensing element being mounted parallelto the plane of said flexible diaphragm and being adapted to detectdeflections of said flexible diaphragm.
 4. A transducer as defined inclaim 3 wherein said flexible diaphragm is a thin metal diaphragm andsaid support means is an elongated cylindrical diaphragm support ringformed integrally with said diaphragm to surround its edges, saiddiaphragm support ring having two ends, and wherein said seal comprisesan 0-ring between one end of said support ring and an interior surfaceof said housing. and wherein said fluid pressure supplying meansincludes having the other end of said diaphragm ring not being sealed topermit fluid pressure in one of said chambers to be supplied to theoutside of said diaphragm support ring.
 5. A transducer as defined inclaim 4 further comprising: a narrow thickened beam portion formedintegrally with said diaphragm and extending diametrically across saiddiaphragm, said cavity extending into one end of said beam.
 6. Adifferential strain gage transducer, comprising: a housing having firstand second cylindrical end plates formed with opposing inner endsurfaces, each having a central inlet bore extending axiallytherethrough; an annular retaining ring secured between said end platesto space apart opposing inner end surfaces; an integral diaphragmsubassembly comprising a thin flexible diaphragm, an elongated diaphragmsupport ring fromed around the outer periphery of the diaphragm tosupport the edges and a narrow thickened beam portion extendingdiametrically across said diaphragm, said diaphragm being mountedbetween said two end plates and spaced from said opposing inner endsurfaces, opposite surfaces of said diaphragm and the adjacent insidesurfaces of said diaphragm ring being in fluid pressure communicationwith the respective inlet bores and the outside of said diaphragm ringbeing in communication with one of said bores; said subassembly beingformed with an opening in said diaphragm ring extending radially fromits outer periphery and terminating in a small cavity extending radiallyinto one end of said beam portion to define opposing walls in a planeparallel to the plane of the diaphragm and extending into said beam; andsensing elements secured to the top and bottom walls of said cavityadapted to detect deflections of said diaphragm due to differences inthe pressures applied through said bores to said diaphragm.
 7. Atransducer as defined in claim 6 wherein the opposing inner end surfacesare formEd on said end plates to match the contours of the adjacentsurfaces of said diaphragm and beam portion and are closely spacedtherefrom to act as mechanical stops for said diaphragm.
 8. Adifferential strain gage pressure transducer, comprising: a housinghaving first and second cylindrical end plates, said end plates eachhaving a flat inner end surface positioned closely adjacent that of theother; an outer retaining ring in the form of a thick walled cylindricalsleeve held between an outwardly flanged outer end portion of said twoend plates maintaining a predetermined spacing between said adjacentflat inner end surfaces; means for securing said two end plates and saidretaining ring together to form a rigid unit; said end plates eachhaving a central fluid inlet bore extending axially from the inner tothe outer ends of each end plate; an integral metal diaphragmsubassembly comprising a thin flat flexible circular diaphragm, a narrowthickened beam portion formed on both sides of said diaphragm andextending diametrically in the same direction across opposite surfacesof said diaphragm, and an elongated annular diaphragm support ringformed around the outer periphery of said diaphragm; said diaphragm ringbeing clamped between said end plates so that the diaphragm is spacedsubstantially midway between said adjacent flat inner end surfaces ofsaid end plates to define separate first and second fluid pressurechambers; sealing means between at least one of said end plates and saiddiaphragm support ring for preventing fluid pressure communicationbetween said first and second fluid pressure chambers; said diaphragmsupport ring being formed to define radial openings communicatingbetween only one of said chambers and the exterior surfaces of saiddiaphragm support ring; a small hollow cavity extending radially intoone end of said beam portion and communicating externally throughenlarged radial apertures formed through the cylindrical walls of saiddiaphragm support ring and said outer retaining ring, said cavityproviding opposite interior walls parallel to the plane of saiddiaphragm; a first pair of semiconductor strain gage elements attachedto one interior wall of said cavity; a second pair of semiconductorstrain gage elements attached to the opposite interior wall of saidcavity; said first and second pairs of semiconductor strain gageelements attached to said opposite interior walls being placedrespectively in tension and in compression by bending resulting fromdeflections of said diaphragm and said beam portion by fluid pressuredifferences in said chambers; and circuit means coupling said first andsecond pair of strain gage elements, with said enlarged apertures beingadapated to receive external input and output electrical connectionsthereto.
 9. A transducer as defined in claim 2 wherein said fluidpressure supplying means comprises a plurality of holes extendingthrough said diaphragm support ring.
 10. A transducer as defined inclaim 3 wherein said fluid pressure supplying means comprises aplurality of holes extending through said support.